CA1191297A

CA1191297A - Primer composition used for adhesion

Info

Publication number: CA1191297A
Application number: CA000397555A
Authority: CA
Inventors: Mitsuo Hamada; Sadami Yasuda
Original assignee: Toray Silicone Co Ltd
Current assignee: DuPont Toray Specialty Materials KK
Priority date: 1981-03-27
Filing date: 1982-03-04
Publication date: 1985-07-30
Also published as: DE3261099D1; EP0061871A1; ES510774A0; AU553803B2; EP0061871B1; US4401500A; JPH0138149B2; AU8196682A; ES8306783A1; JPS57159865A; BR8201731A

Abstract

Abstract A mixture of an alkoxy containing silicon-compound, a hydroperoxide, and organic solvent is a primer composition useful for bonding heat curing silicone rubber, especially fluorosilicone rubber, to a substrate.

Description

PRIMER COMPOSITION USED FOR ADHESION
The present invention relates to a primer composi.tion which has excellent adhesive propertiesD More specifically, it relates to a primer composition suited to adhering silicone rubber of the heat-curing type, particularly fluorosilicone rubber, to various types of substrates, such as metal surfaces.
Fan and Sh~w in Japanese Patent Publication No. Sho 49[1974]-5730 have described using vinyl-tris(tert-butyl-peroxy)silane as a primer for adhering EPDM, EPR, chlorinated polyethylene, or silicone rubber to surfaces of glass and metal. However, ~his primer exhibits drawbacks such as the necessity of long-term heat treatment at an el.evated temperature and pressure. For this reason, Maizumi and Inoue in Japanese Patent No. Sho 50[1975]~35,530, published November :L7, 1975, describes an adhes.ive primer composition which c~n be used as a primer for attaching thermopla~tic resins to each oth~r or attaching thermoplastic resin to glass, metals, or metal oxides at low temperatures in a short period of time. The primer composition of Maizumi and Inoue is composed of vinyltris(tertiary-butylperoxy)silane, an organoperoxide whose half-life is 1 rninute at 130-1.90C, and an inert organic solvent. However, this primer composition of Maizumi and Inoue exhibits slow air-drying and slow thermosetting properties after it has been coated over with a material to be attached. Therefore, the primer layer coated on the material surface moves from one location to another location by press insertion of material during injection- or press-molding processes~ For this reason, this primer composition o~ Maiæume and Inoue exhibits not only drawbacks such as difficulty in achieving uniform adhesion, but also the d.rawback of interfacial delamination which can be detected by inspection of the adhesion properties of silicone rubber, especially fluorosilicone rubber as a material to be attached. For this reason, this primer composition of Maizumi and Inoue is unsatisfactory YY~

2~7 for attachiny silicone rubber to a substrate, especially for attaching fluorosilicone rubber to a substrate.
As a result of extensive investigations to lmprove the above-mentioned drawbacks, -the present inven-tors were able to perfect a primer composition which air dries and cures well, with which an adhesion effect is obtained by thermocompressi.on bonding at compara-tively low temperatures and in a short period of time, and which is effective in adhering silicone rubber -to a substrate, particularly in adhering fluorosilicone rubber to a substrate. We discovered, as described in our Canadian copending application Serial No.
387,573, filed October 3, 1981, entitled "An Adhesive Primer Composition", that using a primer composition comprising a mixture of an organosilicon compound having at least o:ne alkoxy or alkoxyalkoxy radlcal per molecule, v:Lnyltris(terti.ary butylperoxy)silane, ancl or-~anic solvent was an ~xcel:l.en~
primer whlch ove:rcame th~ drawbaclcs. ~e hav~ now mad~ ~l :Eu:rther discovery wh:ich allows ug to ~a]ce a p:ritne:r composl~ion, equally as good as our primer composition described in Serial No. 387,573, without having to make .the vinyl-tris(tertiary-butyl-peroxy)silane and therefore a less expensive primer composition is obtained.
This invention relates to a primer composition for adhering silicone rubber to a substrate consisting essentially of (A) 100 parts by weight o:E an alkoxy containing silicon compound sel.ected from the group consisting o:E an a:lkoxysilane represented by the :Eormu].a RaRbSi(OR )c wherein R is a monovalent radical selected from the group consisting of alkyl radicals, halogenated alkyl radicals, and aryl radicals; R' is a monovalent radical selected from the group consisting of alkenyl radicals and XR3 - radicals in which X is a monovalent radical selected from the group consist.ing of acryloxy radical, methacryloxy radical, N-aminoalkylamino radical, amino radical, N-alkylamino radical, epoxy radical, and mercapto radical, and R3 is a divalent radical selected from the group consisting of hydrocarbon radicals, halogenated hydrocarbon radicals, hydroxyhydrocarbon radicals and ether radicals; R2 is an alkyl radical or an alkoxyalkyl radical; a has a value of 0 to 2 inclusive; b has a value of 0 to 2 inclusive; c has a value of 2 to 4 inclusive; the sum of a + b + c is 4; and partial hydrolysis condensates of at least one alkoxysilane defined above where said condensate contains at least two alkoxy radicals per molecule, (B) from 0.5 to 50 parts by ~eight of a hydroperoxide, and (C) an organic solvent.
The alkoxy containing silicon compound of (A) can be an alkoxysilane or a partial hydrolysis condensate o.E at least one of the alkoxysilanes. The alkoxysilanes are tetraa:lkoxysll.anes, organotrialkoxys:ilanes, or clior~Ja1lod:ialkoxy~ilanes, which can be expressecl by ~h~
general formula RaRbSi(OR )c ~here R is an alkyl radical such as methyl, ethyl, propyl, or octyl; a halogenated alkyl radical such as

3,3,3-trifluoropropyl î or an aryl radical such as phenyl.
R' is an alkenyl radical such as vinyl or allyl; or a radical represented by XR3- where X is a monovalent radical selected from acryloxy radical, methacryloxy radical, N-am.inoalkylamino radical, amino radical, N-alkylamino radical, epoxy radical, and mercapto radical; and R3 is a divalent radical selected from diva].ent hydrocarbon radicals such as methylene, ethylene, propylene, and phenylene, divalent halogenated hydrocarbon radicals such as chloroethylene and fluoroethylene, divalent hydroxyhydrocarbon radicals, and div~lent ether radicals such as -CH20C1I2CH2CH2- , CH2C 2 2 2 C,113 -C112CH20CHCH2-, and -CH20CH2CH20CH2-.
R2 is an alkyl radical such as methyl, ethyl, propyl, butyl, pentyl, octyl, and decyl or an alkoxyalkyl radical such as beta-methoxyethyl. In the alkoxysilane, a can be Z~37 0, 1, or 2; b can b~ 0, 1, or 2; c can be 2, 3, or 4; and the sum of a ~ b + c is 4. Mixtures o~ the alkoxysilanes can be used.
The partial hydrolysis condensate of the alkoxysilanes are siloxanes which can be straight chain, ring structure, branched chain, three-dimensional structures, or mixtures of these structures. The partial hydrolysis condensate is made by partially hydrolyzing one or more o~ the alkoxysilanes such that there is at least two alkoxy radicals per molecule in the resulting condensate. The condensate is usually a liquid at normal temperatures.
The preferred alkoxy containing silicon compounds of (A) are alkoxys:Llanes of the formula R'Si(OR )3 ~nd partial hydrolysis condens~tes with one or more ~' radicals and 3 o~ more alkox~ r~clic~ls per mol~ulc. 'rh~3c preEerred (A) in the primer compositlons o this invention exhibit the best combination of adhesive properties and air dryability.
Examples of aikoxysilanes of ~A) include vinyltrimethoxysilane, methylvinyldimethoxysilane, vinyltriethoxysilane, vinyl-tris(~-methoxyethoxy)silane, ~-methacryloxypropyltrimethoxysilane, ~-methacryloxypropyl-methyldimethoxysilane, ~-methacryloxypropyltriethoxysilane, ~~acryloxypropyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, allylmethyldiethoxysilane, y-mercaptopropyltrimethoxysilane, ~-mercaptopropylmethyl-dimethoxysilane, N-~-(aminoethyl)-~-aminopropyltrimethoxy-silane, ~-aminopropyltriethoxysilane, ~-aminopropylmethyl-diethoxysilane, ~-mercaptopropyltriethoxysilane, mercaptoethyltriethoxysilane, y-aminopropyltrimethoxy-silane, ~-glycidoxypropyltrimethoxysilane, ~-glycidoxy-propylmethyldimethoxysilane, ~-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.

The hydroperoxide of component (B) used in the present inven-tion is represented by hydrogen peroxide, methyl hy~roperoxide, ethyl hydroperoxide, n-butyl hydroperoxide, 2,4,4-trimethylpentyl-2~hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-~utyl hydroperoxide, cyclohexyl hydroperoxide, and 2-methyl-2-cyclohexen-1-yl hydroperoxide. Component (B) is limi-ted to hydroperoxides because organic peroxides such as ketone peroxides, diacyl peroxides, dialkyl peroxides, peroxyketals, alkyl peresters, and percarbonates do not provide adequate adhesive force when present with component (A). Component (B) is an essential component in order to fur-ther :improve the adhesive force when component (~) is also present. The rnixlng ratio is 0.5-50 parts by weight, preferah~ 5-30 p~rts by wei~ht with respect ~o 100 p~rts by welght o~
component (A). When this mixing ratio is less than 0.5 part by weight, a strong adhesive force is not obtained;
when it is more than 50 parts by weight, a decline is brought about in air dryability ancl adhesive strength.
The component (C) used in the present invention is an organic solvent for the purpose oE dissolving the composition of the present invention, and it is selected wlth due consideration to solubility and to its vaporization properties when applied as a primer. Toluene, xylene, benzene, heptane, hexane, rubber solvent, and trichloroethylene, for example, can be mentionecl, but it is not limited to these alone. One variety of orga}lic solvent can be used, or a mixed solvent of two or more varieties can be used. The mixing ratio is not particularly limited because it is advantageous to adjust it to the viscosity suited to application as primer.
The composition oE the present invention is easil~
obtained merely by uniformly mixing the ahove-mentioned components, (A), (B), and tC). But for purposes o improving the material properties of the coat after hardening, one can add various inorganic fillers; for example, fumed silica, precipitated silica, quartz micro c~

powder, diatomaceous earth, calcium carbonate, red iron oxid~, cerium oxide, titanium oxide, alumina, and carbon black, and also conventionally well-known heat resistant a~ents; coloring agen~s, and other additives, such as organic esters of titanic acid. Also, one or more varieties of organosilanes and organopolysiloxanes other than component (A) may be included.
When using the composition of the present invention, it is desirable to adhere the silicone rubber after it has air dried 30 minutes or longer following application to the substrate.
Examples of subs-trates include metals such as iron, aluminum, copper, zinc, stainless steel, brass, and bronze;
plastics such as epoxy resins, vinyl chloride res:Lns, polyester resins, and polyamide resins; and inoryanic materials such as g:Lass, mortar, ancl asbestos. S:ilicon~
rubber which is to be adhered to the substrate is obtained from a heat-curing silicone rubber composition whose principal ingredients are organic peroxides, fillers, and polymers, copolymers, or mixtures thereof, whose repeating units include dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, methylvinylsiloxane, phenylvinylsiloxane, 3,3,3-trifluoropropylmethylsiloxane, 3,3,3-trifluoropropyl-vinylsiloxane, and 3,3,3-trifluoropropylphenylsiloxane. In particular, the primer composition of the present invention is ideal for the adhesion oE fluorosilicone rubber that contains fluorinated hydrocarbon groups such as 3,3r3-trifluoropropy:L groups which are difficult to adhere with ordinary primers.
The composition oE the present invention is especially useful as a primer and is also useful for the adhesion of silicone rubbers other than those mentioned above and for the adhesion of natural or synthetic rubbers to silicone rubber. In addition, it can be used as a coating agent, added to various rubbers, resins, baking paints, etc., as adhesion improvers, and can itself be used as an adhesive, curable material.

Th(? following examples are presented for illustrative purposes only and should not be construed as limiting the present invention which is properly described in the claims. In the examples, "parts" indicates "parts by weight" and the viscosity is the value measured at 25C.
Example 1 - Various primer compositions having the components and mixing ratios shown in Table I were prepared and applied respectively in a thin coat on metal plates of aluminum, phosphor bronze, and stainless steel and then left alone to air dry for 60 minutes at xoom temperature. Other than the ingredients shown in Table I, each of the primer compositions also contained 1000 parts of rubber solvent which is a naptha having a boiling point range of 43C to 140C. ~ 4 mm thick unvulcanized molding of a fluorosilicone rubber composition (LS-422 base manuEactured by Dow Corning Corporation, Midland, Michigan, U.S.A.), to which 0.5%, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexane was added as cross-linking agent, was placed on the primed substrate surface and made to adhere to the metal plate while simultaneously curing the fluorosilicone rubber composition by heating it for 10 minutes at 170C under a pressure of 30 kg/cm2. Then the adhesion state was examined by peeling apart the fluorosilicone rubber and metal plate. Also, the air drying situation 60 minutes after application of the primer to the metal plate was investigated. The ones judged dry to the touch were indicated by O and those judged sticky were indicated with an X. These results are shown in Table I.
* Trademark 3~
~ I

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~r II IIIo *~
X

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o u~ 1 U~ O e ~ ~r-l ul o h-l~ ~1 0 ~ R ~ 1.rl-rl-rl ~1Q~ (I) h X N ~ ~ Q~ ~I r-J 111 11~
~ r-l Q~ a~ O S~~ UlU~ Q~ ~ 0 ~1 X ~I r-l Q~ S-l a)r4 O (U ~
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x o ,¢ a, ~a ~1-, *
¢ *

~12~7 Example 2 Various primer compositions with the components and mixing ratios shown in Table II were prepared; the primer was applied using metal plates similar to those of Example 1 and dried for 60 minutes at room temperature. Other than the ingredients listed in Table II, each primer composition also contained 1000 parts of rubber solvent as defined in Example 1. A 4 mm thick unvulcani~ed molding oî a dimethylsilicone rubber composition (SH-52U manufactured by Toray Silicone Co,, Tokyo, Japan), to which 0.7~
2,4-dichlorobenzoyl peroxide was added as cross-linking agent, was placed on the primed substrate surface, ancl dimethylsilicone rubber was adhered to the metal plate by heating for 5 minutes at 120C at a pressure of 30 kg/cm2.
The adhesion state and air dryability o the primer wexe investigated in the same manner as Example 1, and the results are shown in Table II.

* Trademark ~9~97 1.0 o o ~n _ I Ln Ln I ~

o o I I I o ~ ~ O
O ,~ ~
rl H O Ln L~ I I O I ~ 'K O
r~
u~

~ O O -~
.~~r I o I I ~ ~ O
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O Ln ~K
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X
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o ~ ~ ~ o x o ~ ^
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z ~ a v ~ d ,J rl ~
,1 -,1 ,1t~ ~ F, r l O
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x o ~ C m ~ rl *
11 l O ~ K

29'7 Example 3 The adhesion state and air dryability of the primer composition shown in Tabl~ III (using 1000 parts toluene as organic solvent in each case) were investigated in the same manner as Example 1.
The results are shown in Table III.. Excellent adhesive properties were exhibited in each case.

9~

~ c~
o o h rl O ~ u~
.,1 O c:, * >~
I O ~ * O X
s~ r~ O P ~
(I) ,y ~D
r~
_ H

~:
~:
~: r~
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u~ tn _ ~ ~ 4~ o~
Pl ~4 0 r-l O O # O
Q) cO o I r~ c O
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O
~ ~1 ~
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æ ~ rl ~d ~
r l ul ~ _ rl 0 ~ C) ~d rr~
m ~ ~ ~ X ~rl ~ ~
c~ m ~ ~ a) o ~ d~D ~d t~ I ~ ~ rd N r~ r-l al ~ rl C~ rl O
c~ - ~ - Oo ~ ~ ~ R e o ,~ ~ ~,q ,~ O
Lr)~ rl ~ ~ I O o\
~ ~I ~ X 0 0 ~ O O ,J
m ,1 u r-l O R rC ,1~ ,~ ~ r-l C)- u~- O O ~1 ~1 Q, ~~d ~ ~
R. a) 0 0 Q,t O Ql O ~1 0 ~^
o ~ o ~ o C~ o\
m ~d S l o Q~ O~) O r-l ~U
~7 N ~ r~ ~ ~ ''~ O
~ .~ ~rl C,) h ~ a) ~ ~ -rl ~ ~rl ~ rl O C>- u~- O O ,5~ )~ 0 ~Z I _ _ ~ 1~ 1~ ~ (1) m 0 ~cl 0 ~ r-lrl O m ,1 ~
0 C~ .~ rl ~ ~ 0 ,, ,,~ o U-- o ~ ~ 11 ~ R
n) ~: ~
~ o ~ Q, rl Ql ~ O r-l ~ ~ ~ A~rl ~ c~ ~~ 1 1 ~ C~ ~rl l¢ ~1 r-l OS~ O 0 ~d o a) ~ o a) .
Q ~ .~ ~ ~c x o ~ m 'd r~ O lt ~:1 C~ ~ ¢ ~; *

Claims

Claims:

1. A primer composition for adhering silicone rubber to a substrate characterized in that it consists essentially of (A) 100 parts by weight of an alkoxy containing silicon compound selected from the group consisting of an alkoxysilane represented by the formula RaR?Si(OR2)c wherein R is a monovalent radical selected from the group consisting of alkyl radicals, halogenated alkyl radicals, and aryl radicals; R' is a monovalent radical selected from the group consisting of alkenyl radicals and XR3- radicals in which X is a monovalent radical selected from the group consisting of acryloxy radical, methacryloxy radical, N-aminoalkylamino radical, amino radical, N-alkylamino radical, epoxy radical, and mercapto radical, and R3 is a divalent radical selected from the group consisting of hydrocarbon radicals, halogenated hydrocarbon radicals, hydroxyhydrocarbon radicals and ether radicals; R2 is an alkyl radical or an alkoxyalkyl radical; a has a value of 0 to 2 inclusive; b has a value of 0 to 2 inclusive; c has a value of 2 to 4 inclusive; the sum of a + b + c is 4; and partial hydrolysis condensates of at least one alkoxysilane defined above where said condensate contains at least two alkoxy radicals per molecule, (B) from 0.5 to 50 parts by weight of a hydroperoxide, and (C) an organic solvent.

2. The primer composition according to claim 1 in which the condensate is a liquid organopolysiloxane resin having a viscosity of 2 Pa?s, an alkoxy content of 10 percent by weight, and obtained by the partial hydrolysis of a mixture composed of 60 mol percent methyltrimethoxysilane, 30 mol percent methylvinyldiethoxysilane, and 10 mol percent diphenyldimethoxysilane.

3. A method for adhering silicon rubber to a substrate characterized in that it requires coating the substrate with a primer composition, air drying the coating for at least 30 minutes to form a primer coated substrate, applying a heat curable silicone rubber composition over the primer coated substrate to make an assembly, heating the assembly to a temperature which cures the silicone rubber composition, and a silicone rubber bonded to the substrate is obtained, said primer composition consisting essentially of (A) 100 parts by weight of an alkoxy containing silicon compound selected from the group consisting of an alkoxysilane represented by the formula RaR?Si(OR2)c wherein R is a monovalent radical selected from the group consisting of alkyl radicals, halogenated alkyl radicals, and aryl radicals; R' is a monovalent radical selected from the group consisting of alkenyl radicals and XR3- radicals in which X is a monovalent radical selected from the group consisting of acryloxy radical, methacryloxy radical, N-aminoalkylamino radical, amino radical, N-alkylamino radical, epoxy radical, and mercapto radical, and R3 is a divalent radical selected from the group consisting of hydrocarbon radicals, halogenated hydrocarbon radicals, hydroxyhydrocarbon radicals and ether radicals; R2 is an alkyl radical or an alkoxyalkyl radical; a has a value of 0 to 2 inclusive; b has a value of 0 to 2 inclusive; c has a value of 2 to 4 inclusive; the sum of a + b + c is 4; and partial hydrolysis condensates of at least one alkoxysilane defined above where said condensate contains at least two alkoxy radicals per molecule, (B) from 0.5 to 50 parts by weight of a hydroperoxide, and (C) an organic solvent.